Fuel injection apparatus and method for cylinder injection type internal combustion engine

ABSTRACT

With a cylinder direct injection engine in which fuel is injected directly into combustion chambers and air-fuel mixture is guided by an air flow, it is difficult to secure combustion stability under low engine speed and low load conditions such as during idling. Furthermore, there are needs for improvement of emission characteristics and fuel economy in other operation modes as well. An engine according to the invention injects fuel while dividing the same in plural parts during a compression stroke. The first injection forms a lean air-fuel mixture around an ignition plug, and the second injection makes a flammable air-fuel mixture reach an area around the ignition plug. This ensures efficient stratified combustion and allows improvement in emission and fuel economy performance.

This application is a division of application Ser. No. 09/653,167, Sep.1, 2000 now U.S. Pat. No. 6,557,532.

BACKGROUND OF THE INVENTION

The present invention relates to a cylinder injection type internalcombustion engine that supplies fuel directly into combustion chambersby fuel injection valves.

JP-A-11-159382 describes a technology directed to a cylinder injectionengine (hereafter simply referred to as engine), which comprises fuelinjection valves (hereafter simply referred to as injector) forsupplying fuel directly into combustion chambers and, when the engine isin an operation zone of low engine speed and low load conditions,injects fuel in compression strokes to stratify and burn air-fuelmixture. The technology is for improving fuel consumption by injectingfuel in plural times during a compression stroke, when the engine is inan operation zone wherein at least either the load or engine speed isrelatively high within a stratified combustion region, to thereby extendthe stratified operation zone.

JP-A-7-119507 describes a technology of injecting fuel while dividingthe same in the uniform combustion (synonymous with homogeneouscombustion) region under high load and low engine speed conditions andthus reducing the injection quantity at one time to achieve uniformcombustion through effective atomization and diffusion of fuel.

Both the conventional technologies described above employ injectors withlong-distance spray penetration and use pistons as guides or hit plugsdirectly with fuel. Accordingly, the injected fuel deposits on thepistons in the stratified combustion region or deposits on combustionchamber walls after passing through the ignition plugs, and they cannotimprove fuel economy or reduce emissions as much as theoreticallypossible. Besides, even if fuel is divided and injected in plural timesat one fuel injection timing, much of the fuel contacts the pistons andthe combustion chamber walls due to the character of the system,resulting in insufficient improvement in fuel economy and emissionreduction.

Injectors conventionally used in cylinder injection type internalcombustion engines are driven by high-voltage generators includingcapacitors. In case of driving the injector for opening and closingplural times during one injection timing, time for charging thecapacitor is required while the valve is closed between injections, andthe injection interval cannot be shortened. Accordingly, another problemis that fuel cannot be injected multiple times during one injectiontiming if the duration of the combustion stroke in a high-speedoperation zone is short.

Furthermore, the conventional art described above do not discuss anystratified combustion that takes place in such an engine operation zonewherein a starter is operated. This means that an engine is started witha high air-fuel ratio to avoid combustion failure because a failure instratified combustion under such conditions will result in several timesthe normal amount of HC emissions to make it impossible to meet severeEuropean emission regulations.

However, the higher the air-fuel ratio used for starting, the more HC isemitted. Besides, the conventional art described above do not giveconsideration to the fact that operating the injectors multiple timesduring one fuel injection timing results in heavy power consumption.

BRIEF SUMMARY OF THE INVENTION

It is one of objects of the present invention to enlarge the region ofstratified combustion as compared with the conventional art so as toimprove fuel economy as well as emission characteristics.

Another object of the invention is to improve fuel economy as well asemission characteristics by extending the operation zones in which fuelis injected multiple times during one injection timing.

Still another object of the invention is to lessen power consumptioneven when the injector is opened and closed multiple times during oneinjection timing.

To attain any one of the above objects, according to the first aspect ofthe invention, a fuel injection valve is so constructed that the stateof the current flowing through an electromagnetic coil varies between aValve Starting To Open state and a subsequent Valve Held Open state, andthat the cycle of the Valve Starting To Open state and the Valve HeldOpen state is repeated at least twice during one fuel injection timing.

According to the second aspect of the invention, a fuel injection valveis so constructed that two electromagnetic coils are provided and thestate of the current flowing through them is switched between a ValveStarting To Open state and a subsequent Valve Held Open state, and thatthe cycle of the Valve Starting To Open state and the Valve Held Openstate is repeated at least twice during one fuel injection timing andthe state of the current flowing is switched every time the cycle isrepeated.

Preferably, in the constructions according to the first and the secondaspect, the cycle of the Valve Starting To Open state and the Valve HeldOpen state is repeated at least twice at a given valve closing intervalduring one fuel injection timing.

According to the third aspect of the invention, a fuel injection valveis so constructed as to have a valve element and a valve seat foropening and closing a fuel passage, include a radial fuel passageupstream of the valve seat and extending radially from outside to insidefor imparting a swirling force to fuel and form a fuel flow in theradial fuel passage at least twice during one fuel injection timing,which flows radially from outside to inside.

According to the fourth aspect of the invention, a fuel injection valveis so constructed as to open and close a fuel passage at least twiceduring one fuel injection timing during the operation of a starter.

According to the fifth aspect of the invention, a fuel injection valveis so constructed as to switch between a spraying state of longpenetration and another spraying state of short penetration, use theshort penetration spraying state in a stratified combustion region, usethe long penetration spraying state in a homogeneous combustion region,and inject fuel at least twice during one fuel injection timing when thespray penetration is short.

According to the sixth aspect of the invention, a fuel injection valveis so constructed as to include, in its injection hole, a deflectionelement for deflecting fuel spray in a direction to an ignition plug andinject fuel from the deflection element toward the ignition plug atleast twice during one fuel injection timing.

According to the seventh aspect of the invention, a fuel injection valveis constructed so that an air flow generator, provided in an intakeport, creates an air flow in a combustion chamber, the valve divides andinjects the fuel required for combustion in plural times, and fuel sprayin plural times is guided in a direction to a ignition plug by the airflow.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

FIG. 1 is a perspective view of a tumble guide type cylinder injectionengine;

FIG. 2 is a sectional view of the tumble guide type cylinder injectionengine;

FIGS. 3A, 3B, and 3C are views for explaining differences in spraycharacteristics between single-shot injection and double-shot injection;

FIG. 4 is a table for explaining injection methods in respectiveoperation zones;

FIG. 5 is a graph showing a map of injection methods based on enginespeed and load;

FIG. 6 is a flow chart illustrating how to select an injection method;

FIG. 7 is a schematic view for explaining the construction of an enginecontrol unit;

FIG. 8 is a view for explaining the distribution of weakly stratifiedair-fuel mixture in case of double-shot injection (with a long intervalbetween first and second injections);

FIG. 9 is a view for explaining an air flow toward a plug generated bythe first injection;

FIG. 10 is a view for explaining the distribution of weakly stratifiedair-fuel mixture in case of double-shot injection (with a short intervalbetween first and second injections);

FIG. 11 is a graph for explaining the relationship between crank anglesand air-fuel mixture density near a plug;

FIG. 12 and FIGS. 12A to 12C are a graph and views for explaining theeffect on a spray caused by a cylinder pressure during injection;

FIG. 13 is a graph for explaining the optimum value of injectioninterval D1;

FIG. 14 is a graph for explaining the optimum value of injection rateT2/T3;

FIG. 15 is a graph for explaining the relationship between an injectionperiod and a fuel flow rate;

FIG. 16 shows views for explaining the application of a narrow-anglespray injector to a tumble guide cylinder injection engine;

FIG. 17 shows views for explaining the application of double-shotinjection to an overhead type cylinder injection engine;

FIG. 18 is a view for explaining the application of double-shotinjection to a wall-guide type cylinder injection engine;

FIG. 19 is a view for explaining the application of double-shotinjection to a flat-piston type cylinder injection engine;

FIGS. 20A and 20B are views for explaining the essential part of aninjector;

FIG. 21A is a view for explaining the construction of the injector;

FIG. 21B is a view for explaining the construction of the controlcircuit of the injector;

FIG. 21C is a view for explaining the operation of the injector; and

FIG. 22 is a view for explaining the essential part of a deflected-spraytype injector.

DETAILED DESCRIPTION OF THE INVENTION

An example system of a cylinder injection engine to which the inventionis applied is shown in FIGS. 1 and 2.

The engine 30 is provided with two intake pipes A and B, plates 20separating them horizontally, and air flow control valves 21 at thestart points of the plates 20. These are configured to produce a forwardtumble flow 50 moving from intake valves 10 to exhaust valves 11 and toa piston 31 within a combustion chamber.

The intensity of the air flow 50 can be varied by controlling theopening of the air flow control valves 21 by an electronicallycontrolled actuator 21A through a link 21B. For facilitating retentionof the tumble flow 50, a tumble retention groove 50A for guiding thetumble flow is formed in the top face of the piston 31.

An ignition plug 32 is located at the center of the combustion chamber,and an injector 1 for injecting fuel directly into the combustionchamber is disposed between the two intake valves 10 on the combustionchamber, while being tilted upward at an angle of 30 degrees from thehorizontal with a fuel injection hole facing the cylinder.

The injector 1 comprises a solenoid valve with an electromagnetic coil,and its opening and closing is controlled by the control signals from anengine control unit (hereafter referred to as ECU) 41.

As a fuel injection control signal is input into an injector drivecircuit 40 from ECU 41, an electromagnetic coil 2 of the injector 1,which will be described in detail later, is energized by a battery VB.Upon the energization, a plunger 3 is raised, a valve element 3 aattached to the tip of the plunger 3 leaves a valve seat (not shown),and the high-pressure fuel pressurized by a high-pressure pump (notshown) is injected into the combustion chamber.

The fuel is injected with a swirling force imparted by a swirler 4,which is installed upstream of a valve 3 a of the injection 1.Accordingly, in a intake stroke injection when the pressure in thecombustion chamber is low, the fuel forms a hollow cone-shaped spray.

On the other hand, in a compression stroke injection when the combustionchamber pressure is high, the injected fuel collapses into a solidspray.

In this embodiment, in a stratified combustion region, the spray 60 ainjected first diffuses in the direction of the plug 32, remains aroundthe plug 32, and then burns with a pilot flame of the spray 60 binjected next, as shown in the figure.

In the figure, 32 a denotes an ignition coil, which makes an ignitionspark on the ignition plug 32 in response to an ignition signal from ECU41.

Now the invention will be outlined with reference to FIGS. 3A and 3B.According to the invention, fuel is injected while being divided inplural times at very small intervals during the compression stroke.

A spray in the case of a single shot by an injector with a swirler, orwhen all the fuel needed for combustion is injected at once by a singleopening of the injection valve during one fuel injection timing, haspenetration L1 as shown in FIG. 3A. On the other hand, when the samequantity is divided and injected in two times, sprays have smallerpenetration because of the reduced injection quantity per injection asshown in FIG. 3B.

Comparing the longer of the penetration L2 of the first injection andthe penetration L3 of the second injection with the penetration L1 ofthe single-shot injection, the former L2 (or L3) is shorter.

Making similar comparison for an injector without a swirler upstream ofthe injection valve, for the same fuel supply quantity and the same fuelpressure, the degree of decrease of penetration when the same fuelquantity was divided and injected in two times was larger in the case ofthe invention having a swirler upstream of the injection valve.

Further, it was found that, when fuel was injected twice successively inthe atmosphere of the same pressure, generally high density sprays builtup in a small area as the second spray 60 b arrived to lie over thefirst spray 60 a that has lost its power for straight movement andstagnated.

In actual situations, however, the combustion chamber pressures at thetime when the first injection 60 a is effected and at the time for thesecond injection 60 b are different. The pressure at the time of thefirst injection 60 a is lower than that at the time of the secondinjection 60 b.

By the way, the injector equipped with a swirler produces a hollowcone-shaped spray in a low-pressure atmosphere, and a solid compactspray in a high-pressure atmosphere.

Therefore, in the actual engine, as shown in FIG. 3C, the hollowcone-shaped spray 60 a is injected by the first injection into thecombustion chamber under a low pressure and spreads widely on an airflow because of its light weight. Then, the solid second spray 60 b isinjected by the second injection into the relatively high-pressurecombustion chamber, which does not spread so widely as the first spray60 a and gathers around the plug, because fuel particles are relativelyheavy as well as because the air flow has weakened.

This pressure difference in the atmosphere helps form an ideal air-fuelmixture with a rich air-fuel mixture layer formed around the plug and alean air-fuel mixture formed around the first layer.

When an injection period T1 is long, for instance more than 2 ms, thehollow cone-shaped first spray injected from the injector with a swirleris formed in a bell shape due to a difference between its internal andexternal pressures, making the spray's divergence angles θ1 and θ2 moreacute and thus suppressing the dispersion of the spray. In contrast,when the fuel is divided and injected in plural times, the injectionperiod of each injection is reduced, making it possible to prevent thespray's divergence angles from becoming acute and thus disperse the fuelwidely (θ1<θ2).

With the injector having a swirler, it is possible to control thedivergence angle of a spray by selecting between the single-shotinjection and the double-shot injection where the fuel is divided in twoparts.

FIG. 4 shows the injection pattern according to the invention, and FIG.5 shows the operation zones of the cylinder injection engine to whichthe invention has been applied. In FIG. 5, the abscissa represents theengine speed, and the ordinance represents the load, {circle around (1)}and {circle around (2)} represent homogeneous operation zones, {circlearound (3)} a weakly homogeneous operation zone, and {circle around (4)}and {circle around (5)} stratified operation zones.

In the homogeneous operation zone {circle around (1)} under high loadand high engine speed conditions, a large quantity of fuel has to beinjected in a short period of time. Accordingly, fuel is injected in asingle shot during the intake stroke or during the period from theexhaust stroke to the intake stroke, as shown in row (1) in FIG. 4.Under high engine speed and high load conditions, the air flow in thecombustion chamber is strong, and a spray concentrates on the side ofthe intake valves to lower the utilization factor of air. The use ofsingle-shot injection with strong penetration, which allows sprays toreach the exhaust valves and facilitates mixing, however, improves theoutput and the fuel economy.

In the high load and low engine speed zone {circle around (2)}, fuel isdivided and injected in plural times during the intake stroke, as shownin row (2) in FIG. 4. This reduces spray penetration as well as fueldeposits on the exhaust-side cylinder wall and the piston crown.Moreover, by shortening the injection period at each injection, it ispossible to increase the spray angle of the first injection 60 a andthereby facilitate mixing.

{circle around (3)} is the weakly stratified operation zone whereinwhich fuel is injected while being split between the intake andcompression strokes, as shown in row (3) in FIG. 4. A lean air-fuelmixture is formed around the plug by the injection at the intake stroke,and weakly stratified combustion is achieved using the spray injected atthe compression stroke as a pilot flame for firing.

{circle around (4)} is the stratified operation zone under a relativelyhigh engine speed condition, in which fuel is injected all at once or ata single shot during the compression stroke, as shown in row (4) in FIG.4, to achieve stratified combustion.

In the stratified operation zone {circle around (5)} under low load andlow engine speed conditions, the fuel sprays caused by multipleinjections during the compression stroke, as shown in row (5) in FIG. 4,are guided by the air flow. This realizes stable stratified combustionin the region where stable stratified combustion is difficult to attainby any conventional engine. As a result, the stratified combustionregion is extended as compared with the conventional art to enable theimprovement of fuel economy and the reduction of emissions.

In the multi-shot (double-shot) injection on during the compressionstroke shown in row (5) in FIG. 4, the first injection is done from thebeginning to the middle of the compression stroke to form the layer 60 aof lean air-fuel mixture near the plug as shown in FIG. 8. Then, thesecond injection is carried out from the middle to the end of thecompression stroke to ignite and burn the spray 60 b when it reaches theignition plug.

Since the ignition plug is surrounded by a layer of flammable air-fuelmixture, a layer of lean air-fuel mixture is around the first layer anda layer of air surrounds the second layer, the air-fuel mixture burnsefficiently. Further, no air-fuel mixture exists near the wall surfaces,and HC production is reduced in the quenching layer which does not lenditself to flame propagation. This achieves a reduction in HC emissions.

In this case, the second injection is performed at a latter stage of thecompression stroke when the air flow is very weak, and if usingconventional systems, the spray does not have enough penetration toreach the plug. According to the invention, however, the secondinjection can reach the plug because of the reason described above andbecause the first injection produces a flow in the direction of the plugas shown in FIG. 9 and the second injection is dragged by this flow.This extends the stable combustion region and further improves fueleconomy.

By making the interval between the first and second injections veryshort (around 1.5 ms) in the double-shot injection at the compressionstroke shown in row (5) in FIG. 4, it is possible to prolong the timewhich is required for the air-fuel mixture to pass the plug, as shown inFIG. 10.

In a so-called tumble guide engine in which fuel is conveyed to theignition plug by means of a tumble flow, air flow mixture can beinjected only during the period when it passes the ignition plug.Accordingly, optimization of the timings of the first and secondinjections causes sprays to pass the ignition plug twice successivelyand enables ignition at both the timings to extend the zone of stablecombustion region.

As described above, with the multi-shot injection at the compressionstroke, controlling of the interval between the first and secondinjections provides two effects that are the improvement of fuel economy(air-fuel mixture curve 60 in FIG. 11) through the weak stratificationof air-fuel mixture and the extension of the stable combustion region(air-fuel mixture curve 61 in FIG. 11) through the prolongation of theperiod in which air-fuel mixture passes the ignition plug.

Furthermore, in the situation where catalysts are not warmed upsufficiently at the time of starting, fuel is injected at thecompression and expansion strokes, as shown in row (6) in FIG. 4. Leancombustion is carried out at the compression stroke, fuel is furtherinjected at the expansion stroke, and the second spray is burnt usingthe excess air and combustion heat from the first combustion, to raisethe exhaust gas temperature and reduce the warm-up time of thecatalysts. Early activation of the catalysts enables exhaust emissioncontrol to serve for reducing emissions.

In this zone, air itself does not move much, and the effect of guidingfuel by air flow is little. Therefore, the fuel injection periods shouldbe made longer than those in the other double-shot injection zones so asto extend penetration and thus make it easier for the sprays to reachthe area around the plug.

During starting, in such a low engine speed zone that the engine isdriven by a starter, fuel is injected, for initial combustion, into thecylinder where the piston is at rest halfway in the compression stroke.In this case, the use of the multi-shot injection at one injectiontiming according to the invention makes it possible to provide directfuel injection apparatus that can effect the starting with stratifiedcombustion from the beginning, is less in production of HC and realizesgood fuel economy.

Usually, fuel pressure and injection rate at the time of starting arelow, and the injection period has to be made a few times longer thanthat for the normal operation. With conventional direct fuel injectionapparatus, fuel spray penetration is so large that fuel tends to depositon the opposite wall or overshoot the ignition plug at the timing ofignition. Further, in such an operation condition, there is a problemthat fuel pressure is low and fuel atomization is insufficient.Consequently, stratified combustion cannot be achieved, and the engineis started by homogeneous combustion.

This embodiment operates the injector twice at one injection timing,divides and injects fuel which is of the quantity for one injection inthe conventional apparatus. This enables reduction of penetration, whichin turn prevents fuel from depositing on the opposite wall. Also, fuelis atomized sufficiently even under low pressure because of the smallfuel quantity. Consequently, the engine can be started with stratifiedcombustion from the initial ignition.

As shown in FIG. 7, the ECU 41 receives the signals of the temperatureof engine cooling water, temperature of engine lubricant, engine speed,load, throttle position, rotation angle of the crankshaft, A/F (outputfrom an air-fuel ratio sensor or oximeter), etc. from various sensorsinstalled on the engine, and determines the condition of the engine.Further, the ECU selects an injection method in accordance with the flowchart in FIG. 6, and outputs the injection timing, injection period,ignition timing, etc. to the injector drive circuit 40 and an ignitioncircuit 32 a. 32 b in FIG. 2 denotes the ignition coil.

Although the combustion chamber pressure varies little between twoinjection timings during a homogeneous operation, it varies during astratified operation as shown in FIG. 12. The rate of change is afunction of the injection timing, engine speed, and amount of intakeair, and the injection interval has to be determined according to theseconditions.

When the injection interval (time) is constant, judging on the basis ofthe state shown in FIG. 12B, under the condition shown in FIG. 12A inwhich intake air is abundant, the combustion chamber pressure at thetime of the second injection is high and the spray is compact.Accordingly, there is a possibility that a space is given between thefirst and second sprays and they are separated from each other.

In the case of the low engine speed condition shown in FIG. 12C, thereis not much pressure change, and the result is considered to be close tothat of a steady-state spray testing.

To obtain the optimum air-fuel mixture for combustion, the injectiondwell interval D1 between the first and second injections is shortenedaccording as the engine speed and the amount of intake air increase oraccording as the injection timing is retard, as shown in FIG. 13.However, D1 must not be shorter than the time (approximately 1.5 ms)needed to charge the capacitor of a booster circuit that supplies powerto the injector.

As shown in FIG. 14, T2/T3 is decreased according as the engine speedand the amount of intake air increase or according as the injectiontiming is retard. In other words, T3 is extended. However, T2 must belarger than the ineffective injection pulse width shown in FIG. 15.

FIG. 15 shows the relationship between the injection period and the fuelflow rate, and it can be seen that they are almost in direct proportion.However, shortening of the injection period causes a region where thechange in the flow rate is not linear due to a lag in opening of aninjector plunger and due to the instability of plunger operation.

An injection interval in the non-linear region is referred to as anineffective injection pulse width and is not used. If the injectionpulse width (injection interval) falls within this region, the fuelpressure is lowered to reduce the flow rate and the injection pulsewidth is prolonged to make up for it.

The engine according to the first embodiment employs the injector withthe swirler, which is a wide-angle spray injector, to provide a sprayangle large enough for the spray to reach the plug. It uses themulti-shot injection at the compression stroke in low engine speed andlow load zones where relatively large penetration is required.

The second embodiment is shown in FIG. 16. Employed in this embodimentis a narrow-angle spray or solid-spray injector, which can providerelatively large penetration. Fuel is injected all at once at oneinjection timing under low engine speed and low load conditions with ashort injection period. Under medium engine speed conditions in whichtoo large penetration poses the problem of deposits on wall surfaces,and fuel is injected twice at one injection timing.

The use of the narrow-angle spray injector enables the formation of fuelsprays that readily diffuse in spite of strong downward flows from theintake valves even under homogeneous and high load conditions.

Under low load conditions, in which injection pulses are short, if aninjection is split in two, the injection pulse width of one injectionmay become less than the ineffective injection pulse width. In such azone, it is useful to lower the fuel pressure and increase the injectionpulse width.

The third embodiment is shown in FIG. 17. This has a structure in whichan injector is disposed aside the ignition plug in the center of thecombustion chamber, not on the side of the engine head. During astratified operation, double-shot injection at the compression strokesuppresses penetration. Accordingly, it is possible to reduce depositson the piston crown surface and make a two-layered air-fuel mixture toprovide an ideal mixing condition.

Moreover, since fuel is injected from the center of the combustionchamber, the air-fuel mixture does not pass through and stays in thecenter, ensuring stable combustion in wide ranges of injection andignition timings. During a homogeneous operation, the spray conforms tothe shape of the combustion chamber, ensuring effective use of air. Alsoin the homogeneous operation, double-shot injection at the compressionstroke makes it possible to reduce deposits on wall surfaces through thesuppression of penetration and to facilitate mixing through theexpansion of spraying.

In the case of an injector that is operated by boosting a batteryvoltage with a booster and applying the high voltage to a coil, a longinjection interval should be provided in order to open the injectormultiple times in a short period of time at close intervals. This isbecause time is required to charge a capacitor with the battery voltage.If the capacitor is not charged to a sufficient voltage, the secondopening of the valve may be delayed, resulting in inability to provide arequired injection quantity. Usually, an interval of approximately 1.5ms or more is required.

With the use of an injector that can be operated at the battery voltageis used, there is no need for voltage charging, and multiple injectionscan be performed at very close intervals. In this case, it is possibleto extend the stable combustion region by injecting fuel twice at closeintervals at the compression stroke even in the high engine speed zoneof stratified combustion.

Furthermore, in an engine equipped with a 42-V battery, a fuel flow isstable even if the pulse width is smaller, the above method allowsmultiple injections without lowering the fuel pressure even in low loadzones.

Although the embodiments have been described in relation to the enginesin which air-fuel mixture is guided by air to be stratified, theinvention is applicable also to such a construction as shown in FIG. 18,in which air-fuel mixture is guided by a piston cavity 180.

In a cylinder injection engine whose piston has a flat crown surface asshown in FIG. 19, the fuel injected from the injector 1 directly hitsthe ignition plug 32 to form air-fuel mixture.

The injector 1 used is, for example, a solid-spray injector that makesthe shape of a spray difficult to alter with changes in the cylinderpressure. It is important, in particular, that the spray angle in thedirection of the ignition plug does not change. This will ensure thatthe fuel reaches the ignition plug without being affected by theinjection timing and the engine speed.

Further, the piston has a flat shape without a cavity. This reducescooling loss and intake loss on the piston crown surface, resulting inimproved fuel economy.

In the engine of this construction, the time during which a spray passesthe ignition plug is short, but it is possible to extend the time duringwhich air-fuel mixture stays around the ignition plug and thus expandthe stable combustion region by dividing injection in multiple timesduring one injection timing and properly adjusting the interval betweenthe first and second injections.

Also, the division of injection in plural times at one injection timingenables the reduction of penetration. Accordingly, it is possible toreduce deposits on the wall surface on the side of the exhaust valves toimprove fuel economy and exhaust emissions.

The embodiments have been described above in relation to the injectorwith the swirler or the solid-spray injector, the invention isapplicable also to a hole-nozzle injector, a plate-nozzle injector andthe like. Further, although the embodiments have been described as theexamples of splitting an injection in two times, it is also possible todivide an injection into three or more times.

The detailed construction of the injector with the swirler used in theinvention and that of the injector operated at battery voltages will bedescribed with reference to FIGS. 20A, 20B, 21A, 21B, and 21C.

FIG. 20A is an enlarged view of an injector nozzle tip, in which theswirler 117 according to the invention is illustrated. In the swirler117, axial grooves 212 and radial grooves 221 are formed, and further anannular space 251 is formed at the outlets of the radial grooves 221.

Each axial groove 212 consists of a passage with a semi-lunar crosssection which is defined by the plane axially cut in the side face ofthe cylinder of the swirler 117 and by the cylindrical inner surface ofthe nozzle. These axial grooves 212 and the radial grooves 221 are thepassages for the fuel introduced from above. The fuel that has passedthe axial grooves 212 is led eccentrically with respect to the valveaxis by the radial grooves 221 into a swirl space 231 upstream of avalve seat. This imparts a so-called swirling force to the fuel.

In this construction, the spray angle, i.e., the divergence angle of thefuel injected from the nozzle 208 can be controlled by adjusting anoffset L (the distance between the valve axis and the center of theradial groove, shown in FIG. 20B), width, and/or depth of the radialgroove 221 in the swirler 117. Although decreasing the offset L of theradial grooves 221 or increasing the width or depth of the grooves makesswirling flows prone to be generated, the annular space 251 has theeffect of decreasing the variations in the swirling fuel.

The annular space 251 has a larger diameter as compared with the fuelswirling space 231 located downstream of it. Accordingly, even when theflow rate of fuel passing along the radial grooves 221 is decreased, itis possible to increase the swirling force and consequently use theswirl space effectively by increasing the offset L of the radial grooves221. This makes it possible to obviate the variations as well as topositively facilitate mixing of the fuel.

As a valve 116 leaves the valve seat 210 twice at one injection timing,fuel flows each time through the axial grooves 212, the radial grooves221, the annular space 251, the swirl space 231, and the injection hole190, and is injected into the combustion chamber.

During the valve closing interval between the first and secondinjections, the fuel stays exclusively in the annular space 251 waitingfor the second injection to take place reliably from the beginning.

If no such annular groove is provided, when the valve repeats openingand closing in a short period of time, fuel supply may fail to keep pacewith the operation, resulting in fuel starvation.

The fuel injection valve used in the invention supplies fuel radiallyfrom outside to inside through the radial grooves 221 plural timesduring one injection timing. The valve does not change in its swirlingeffect on fuel even when the split spraying at high speed and performsstable atomization at the fuel nozzle, enabling stable fuel injectioninto the high-pressure combustion chamber.

Thus, the fuel injection valve of the invention provides the fuelatomization effect in the split injection and the fuel supplyresponsibility for high-speed valve operations, which are not possiblewith injectors without a swirler.

Embodiments of the injector and the fuel injection apparatus accordingto the invention will be described with reference to FIGS. 21A, 21B, and21C.

FIG. 21A is a sectional view showing the overall structure of theinjector 1 (an enlarged view of the tip nozzle is shown in FIG. 20A),and FIG. 21B is a schematic diagram showing the wiring configuration ofthe fuel injection apparatus (the injector 1 and the injector drivecircuit 40).

At the outset, the structure of the injector 1 will be described withreference to FIG. 21A. The injector 1, to which pressurized fuel issupplied by a fuel pump, opens and closes the fuel passage between theball valve 116 serving as a valve element and a seat surface (valve seatsurface) 210 formed on the side of a yoke casing 114 to control theinjection quantity of the fuel from the fuel injection hole 190.

The ball valve 116 is attached to the tip of a plunger 115, and theswirler 117 for fuel atomization is installed close to and upstream ofthe seat surface 210.

As a means for generating a driving force for the ball valve 116, theinjector 1 is equipped with a control coil 111 and a holding coil 112.These coils, when energized, generate magnetic fluxes, forming amagnetic path passing through a core 113, a yoke 114, and the plunger115. As a result, an attractive force is created between the facing endsof the core 113 and the plunger 115.

By this force, the plunger 115 and the ball valve 116 move in thedirection away from the seat surface 210 (to the right in the figure),and fuel is injected. On the other hand, when no attractive force by thecontrol coil 111 and the holding coil 112 (i.e., in the state of nocoils energized), the ball valve 116 is pressed against the seat surface210 by the spring force of a return spring 118 through the plunger 115,and the injector 1 is in the valve close state.

The control coil 111 and holding coil 112 are electrically connected attheir one ends to form a terminal B. The other end of the control coil111 provides a terminal C, and the other end of the holding coil 112provides a terminal H.

The winding and wiring of the two coils are set such that magneticfluxes are generated in the same direction (in the direction ofreinforcing each other) on the control coil 111 and the holding coil 112when the terminal B is connected to the positive terminal of a batteryand the terminals C and H are connected to the negative terminals of thebattery. The figure illustrates the wiring schematically.

The wiring configuration of the injector drive circuit 100 will bedescribed with reference to FIG. 21B. In the figure, as concerns theinjector 1, shown are the core 113, the control coil 111, and theholding coil 112.

The injector control circuit 100, to which the battery voltage from thebattery VB is supplied, controls the energization of the control coil111 and the holding coil 112, based on the injection signal from theengine controller 41.

The injector control circuit 100 has a holding coil transistor ON/OFFcircuit 104 that controls the energization of the holding coil 112, anda control coil transistor ON/OFF circuit 114 that controls theenergization of the control coil 111.

These transistor ON/OFF circuits share the information about the currentto each coil, which is detected by a holding coil current detectionresistor 103R and a control coil current detection resistor 113R. Thetransistor ON/OFF circuits send an energization signal to a powertransistor 102 t for the holding coil and a power transistor 112 t forthe control coil according to this information and responsive to theoutput of a signal processing circuit 120 which is based on theinjection signal from the engine controller 41.

When the power transistor 102 t for the holding coil and the powertransistor 112 t for the control coil are turned on, the voltage of thebattery BV is applied to the holding coil 112 and the control coil 111.101R and 111R denote the internal resistance of the holding coil 112 andthe control coil 111 and the equivalent resistance of the drive circuit,respectively.

The control coil 111 and the holding coil 112 have different electricalcharacteristics. This is because the control coil 111 and the holdingcoil 112 play different roles in the phases of closing, opening, holdingopen, and closing the valve. In this embodiment, the control coil 111 isused exclusively in the Early Valve Opening state and the holding coil112 is used in the Valve Held Open state.

The difference between these coils will be described below. First, thecharacteristics required of the coils when the valve is opened will bedescribed below.

When the valve is opened, the setting load due to the return spring 118described above and the fuel pressure of the pressurized fuel act on theball valve, resulting in a large checking force against the valveopening operation. Only when the electromagnetic force develops largeenough to overcome these forces, the plunger 115 starts displacement.Thus, it is necessary to minimize the time required to generate theforce because it affects the delay in the valve opening operation.

Magnetomotive force is the product U (=NI) of the number of coil turns N(T) times inflowing current I(A) and can be used to assess the magneticforce attainable in a small amount of time Δt. If internal resistance ofthe drive circuit is zero (0), the smaller the number of turns, thesmaller the inductance component and the resistance component become andthus the larger amount of current flows. Consequently, an increasinglylarger magnetomotive force can be attained in a small amount of time Δt.

Magnetomotive force decreases with decrease in the number of coil turns.However, since coil inductance is proportional to the square of thenumber of turns, it was learned that the increase in current due todecrease in inductance is larger than the decrease in magnetomotiveforce due to decrease in the number of turns. Thus, in order to obtain alarge magnetic force for opening a valve when operating on a low voltagesuch as a battery voltage, it appears more desirable, in terms ofimproving response characteristics, to gain magnetomotive force by meansof current rather than by means of the number of turns.

Actually, however, in the drive circuit exists an internal resistance,which limits the maximum ultimate magnetomotive force as well as changesthe optimum number of turns.

Furthermore, the ease with which current flows is affected not only bythe coils in the injector, but also by the internal resistance of thecontrol circuit, the resistance of switching devices, and any voltagedrop. Therefore, it is necessary to minimize the internal resistance ofthe control circuit, the resistance of the switching devices, andvoltage drops.

The coil used to open the valve, i.e., the control coil 111 according tothis embodiment, and the power transistor 112 t for the control coil 111are constructed as follows.

First, the winding wire of the control coil 111 is a wire with lowresistance and a large diameter. Besides, a bipolar, CMOS, or bi-CMOStransistor is used as the power transistor 112 t to reduce theon-resistance at power-on and the equivalent internal resistance 111R ofthe control coil circuit.

Then, according to the resistance value of the internal resistance 111Rdetermined based on the above-described construction, the number ofturns is determined such that a magnetomotive force close to the maximumultimate value will be attained.

Normally, a smaller magnetomotive force is needed to hold the valve openthan to open it. This is because when the valve is open, the pressuresat the front and rear of the ball valve 16 are balanced as a result offuel injection, reducing the force resulting from the fuel pressure, andat the same time, the air gap enclosed by the core 113, the yoke 114,and the plunger 115 is reduced, raising the magnetic flux density in theair gap and consequently resulting in effective use of the magnetomotiveforce.

When the valve is closed following the period of holding the valve open,as the voltage application is terminated, the magnetomotive force lowersfrom that used to hold the valve open. The magnetic force is lowered,and when it becomes below the setting load of the spring 118, the valvebegins to close. If the magnetomotive force used to hold the valve openis too large, however, there will be a delay in the valve closingoperation.

Therefore, when holding the valve open, the minimum necessarymagnetomotive force should be used.

The coil used to hold the valve open, i.e., the holding coil 112according to this embodiment, and the power transistor 102 t for theholding coil 112 are constructed as follows. First, the internalresistance of the holding coil 112 need not be made particularly small,and the wire diameter may be selected by giving priority to the spacefactor.

In this embodiment, the control coil 111 has the characteristicsrequired to open the valve, and the holding coil 112 has thecharacteristics required to hold the valve open. Simply switchingbetween those coils and energizing the selected coil enables idealoperation in individual phases.

Regarding the layout of the control coil 111 and the holding coil 112 inthe core 113 and the yoke 114, it is desirable to place the control coil111 nearer to the plunger 115. This is because, in the magnetic circuitconsisting of the core 113, the yoke 114, and the plunger 115, magneticfluxes concentrate near the coils. It is advantageous to place thecontrol coil 111, in which a large magnetomotive force is generated atan early stage, nearer to the plunger 115 when the valve openingoperation wherein a particularly large magnetic force is required. Thisembodiment can achieve a wide dynamic range that serves as a performancecriterion.

To extend the dynamic range, it is necessary to keep the minimuminjection flow rate at a low level. The injection quantity is controlledby the actuation time of the injection signal, and the length of theinjection signal that gives the minimum injection flow rate is reducedto the minimum. To keep up with this short injection signal, delays invalve opening and closing operations should be reduced. That is achievedas follows in this embodiment.

The energization of the control coil 111 stops at Tp, but theenergization of the holding coil 112 continues until the injectionsignal falls, i.e., until the valve close signal is issued after Tp.

At the time to start closing the valve, the smaller the current valuesof the coils 111 and 112, the faster the fall of magnetic fluxes, whichis advantageous in reducing the delay in the valve closing operation.The magnetomotive force of the holding coil 112, in particular, isslower to fall than that of the control coil 111, so it is desirablethat the current of the holding coil 112 should have the minimumnecessary intensity.

The electrical characteristics of the holding coil 112 is determinedsuch that the magnetomotive force reached in a small amount of timeafter the voltage application to the control coil 111 is large enough togenerate the magnetic force needed to open the valve.

The holding coil 112 need not be turned on simultaneously with the inputof the injection signal. It is all right if there is some delay. Theattainable current during the fall of the injection signal for theholding coil 112 can be lower than when the coil is turned onsimultaneously with the input of the injection signal. In this way, bydelaying the energization of the holding coil 112, it is possible toreduce the current during the fall of the injection signal, i.e., duringthe valve close instruction, and thus reduce the delay in the valveclosing operation.

In the invention, the current flow to the control coil 111 and holdingcoil 112 with the predetermined characteristics is interrupted twiceduring one injection timing.

The fuel injection apparatus constructed as described above operates asfollows (see FIG. 21C). First, the ECU 41 outputs an injectioninstruction Tsg to the drive circuit 40 plural times depending on theoperational status of the engine.

For the first injection T2, the drive circuit 40 turns on the powertransistor 112 t for the control coil and the power transistor 102 t forthe holding coil from the signal processing circuit 120 through thecircuit 114. The total current as viewed from the battery is indicatedby bold lines in the lower part of FIG. 20C.

The transistor 112 t is turned off when time t2 elapses after it isturned on. On the other hand, the transistor 102 t is kept on during theperiod T2 of the first injection. Consequently, the valve opened by thesum of the magnetomotive forces of the two coils is held open by theholding force of the coil 111. During this time, fuel is injected intothe combustion chamber through the swirler.

When the time T2 elapses, power supply to the transistor 102 t is alsostopped. Accordingly, the coils are demagnetized, the plunger 115 isforced back by the return spring 118, and the valve 116 sits on thevalve seat 120, closing the injection hole.

Then, after a very short interval t4 of valve closure, the drive circuit40 again turns on the power transistor 112 t for the control coil andthe power transistor 102 t for the holding coil from the signalprocessing circuit 120 through the circuit 114, for the second injectionT3. The total current as viewed from the battery is indicated by boldlines in the lower left part of FIG. 20C.

The transistor 112 t is turned off when time t3 elapses after it isturned on. On the other hand, the transistor 102 t is kept on during theperiod T3 of the second injection. Consequently, the valve opened by thesum of the magnetomotive forces of the two coils is held open by theholding force of the coil 111. During this time, fuel is injected intothe combustion chamber through the swirler.

When the time T3 elapses, power supply to the transistor 112 t is alsostopped. As a result, the coils are demagnetized, the plunger 115 isforced back by the return spring 118, and the valve 116 sits on thevalve seat 120, closing the injection hole and ending the secondinjection. In this embodiment, although the injector is operated at ahigh speed, it can be operated at the supply voltage.

Furthermore, since the valve is held open by a small holding currentafter it is opened, the injector can be opened and closed two or moretimes during one injection time without much power consumption.

If the battery VB is 42 volts, the drive current can be loweredaccordingly. Or if the current is not lowered, the number of coil turnscan be reduced and thus the injector can be made smaller.

Each of the injectors of different types described above can beconfigured to combine their characteristics. For example, the injectorwith the swirler may comprise a battery-driven, two-coil injector. Alsothe solid-spray or narrow-angle spray injector may comprise abattery-driven, two-coil injector.

Whatever injector is used, it can be constructed as a deflected-sprayinjector that is equipped at its tip with a deflection element 199 fordeflecting a fuel spray toward the plug, as shown in FIG. 22. In thisembodiment, the deflection element 199 is formed as a protrusion with afuel delivery passage 198 whose central axis is tilted at an angle δfrom the central axis h1 of the injector in the direction of mounting ofthe plug.

This injector can supply a deflected spray toward the ignition plug atleast twice during one fuel injection timing. This constructioneliminates the need for guide mechanisms such as air or piston cavity.

Therefore, it can be used in combination with a piston that has a flatcrown surface. Also, there is no need to install tumble flow generatorsat the intake ports.

The present invention can extend the stratified operation zones for acylinder injection engine. The other aspect of the invention can improvecombustion stability, fuel economy, and emission characteristics bycontrolling air-fuel mixture formation variously according to operatingconditions. The still other aspect of the invention can realize a systemwith low power consumption.

1. A fuel injection apparatus for cylinder injection type internalcombustion engines, which includes a fuel injection valve for injectingfuel directly into a combustion chamber and which is adapted to switch astate of combustion between stratified combustion and homogeneouscombustion, wherein said fuel injection valve is constructed to switchbetween a spraying state of long penetration and another spraying stateof short penetration, switches to the short penetration spraying statein a specific region of the stratified combustion, switches to the longpenetration spraying state in a specific region of the homogeneouscombustion, and injects fuel at least twice during one fuel injectiontiming in the state of short penetration.
 2. An in-cylinder injectiontype internal combustion engine comprising at least one combustionchamber into which air is inhaled, at least one fuel injection valve forsupplying fuel directly into said combustion chamber, said valve havinga fuel swirler upstream of a valve seat, an ignition plug for ignitingfuel, a piston for changing volume of said combustion chamber, a flowgenerator provided on an intake port to generate an air flow in thecombustion chamber so that spray is guided to said ignition plug by theair flow, and injection control means for controlling fuel injectionsuch that fuel required for one injection is injected from said fuelinjection valve while being divided in plural times by valve opening andclosing successively in plural times whereby at least one of penetrationof the spray and injected fuel is substantially prevented from reachingthe piston.
 3. The engine according to claim 2, wherein said injectioncontrol means controls respective injection timings such that the spraydivided into plural parts passes the ignition plug continuously withoutinterruption.
 4. The engine according to claim 2, wherein said injectioncontrol means controls fuel injection timing such that a flow of fuelspray from the fuel injection valve to the ignition plug is generated ina first injection and that another fuel spray by a next injection isguided to the ignition plug by the fuel flow.
 5. The engine according toclaim 2, wherein said injection control means controls such that fuel isinjected by opening the valve one time during one fuel injection timingwhen the engine is under low engine speed and low load conditions, andsaid fuel injection valve comprises a narrow-angle fuel injection valvethat provides penetration only enough for the fuel spray to reach theignition plug.
 6. An in-cylinder injection type combustion enginecomprising at least one combustion chamber into which air is inhaled, atleast one fuel injection valve for supplying fuel directly into saidcombustion chamber, said valve having a swirler upstream of a valveseat, an ignition plug for igniting fuel, a piston for changing volumeof said combustion chamber, and injection control means for controllingfuel injection such that fuel required for one injection is injectedfrom said fuel injection valve while being divided in plural times byvalve opening and closing successively in plural times during acompression stroke in a stratified operation zone under low engine speedand low load conditions and at least one of penetration of spray formedby the swirler and the injected fuel is substantially prevented fromreaching the piston.
 7. The engine according to claim 6, wherein saidinjection control means controls respective injection timings such thatthe spray divided into plural parts passes the ignition plugcontinuously without interruption.
 8. The engine according to claim 6,wherein said injection control means controls fuel injection timing suchthat a flow of fuel spray from the fuel injection valve to the ignitionplug is generated in a first injection and that another fuel spray by anext injection is guided to the ignition plug by the fuel flow.
 9. Theengine according to claim 6, wherein said injection control meanscontrols such that fuel is injected by opening the valve one time duringone fuel injection timing when the engine is under low engine speed andlow load conditions, and said fuel injection valve comprises anarrow-angle fuel injection valve that provides penetration only enoughfor the fuel spray to reach the ignition plug.